We have a bilevel, 3/4 finished lower level, the utility room is concrete. Prior owners had put carpeting downstairs, did not have central air and never used a dehumidifier. Shortly after we moved in, every time it got really humid or rained, the smell of mildew was really unpleasant in the lower level carpeted rooms. Too much moisture in the carpet. We yanked up the carpet and put down laminate with a rubber underside for use on concrete, and replaced the carpeted stair treads with new oak, and the smell has not recurred since. (I was certain we'd find moldy padding, but we didn't.)

Does the smell dissipate if you close the windows and run the furnace fan or AC and a dehumidifier?

If it really bowls you over, you might be looking at sewer or plumbing issues. With regard to plumbing: Do you by chance use the upstairs bath primarily, and have a secondary bath in your lower level that doesn't get as much use? I ask because of a situation we encountered. We have a rental property that had senior tenants. She swore she smelled a foul smell after rain, but he didn't. No one else could detect it either. I happened to have a plumber out routing the basement line and mentioned the smell to him, he said the pipes in the basement were all "open" and good. She insisted it still smelled, primarily from the tub. I was talking to the town's water department engineer one day about a different matter, mentioned this to him. He asked a bunch of questions, turns out they were not running enough water through the lines. (They were on the frugal side, opting for sponge bathing more than showering. ) He suggested I fill up the tub and all sinks with hot water and liquid Lysol (a full bottle in the tub, split another bottle between the sinks). He told me be sure to force plenty of lysol/water into the overflow drain at the top of the tub and sinks as well. I did this, then let everything drain and ran fresh water through after the Lysol. He said plumbing needs to be kept "moist", or gases will accumulate. He said homeowners should do this procedure (fresh water is OK, lysol mainly for first use) at least weekly in bathrooms/sinks/showers that are not used at least several times a week.
But if it's sewer gas, that can be very serious to your health. Maybe check with the plumbing forum here?

Thanks to both of you for the input. We have engineered hardwood over the concrete, so it's not a carpet issue. I tried pouring liquid lysol then running lots of water down the bathroom sink, but the smell is still pretty strong. It's been sunny with no rain here all of today, and the stink is still there. The crawl space doesn't smell at all. We installed a new sump pump before we finished the basement, so I'm not sure what it could be. It's very fishy (literally and figuratively).

We solved the mystery. It was the cheap recessed lighting in the basement...the plastic globes were overheating and starting to melt because we the lightbulbs we had in were high wattage. I guess the reason it seemed worse after rain was that the kids spend more time down there when it's raining and the lights were always on.

Ah, that's a new one ;) Glad you found the source of the trouble, a very tricky one to track down, no less!

I am experiencing a similiar issue, did you have to replace the fixtures or did you opt for lower wattage bulbs? Were you able to fix the problem? Thanks!

We had this same dead animal smell or rotten fish smell in our basement when we were trying to sell our home. It only came when we had showings (when we would turn the lights on) so I googled the smell and issue and luckily came accross this thread. We too had recessed lighting in the basement and the bulbs (only 60 watts) were browning and slightly melting the plastic casings. Very easy fix. If you turn the lights off and probably to be safe the power too, and then unhook the springs that hold the plastic part of the recessed lights up the plastic piece will come down. Take them to Lowes or Home Depot and match them up with new ones. Before you install the new ones there is a nut to adjust the part of the recessed light that holds the bulb; the lower the better as the bulb should stick out from the ceiling I was told by someone who knows how to install properly. If the part that holds the bulb holds the bulb too far up the heat has no way to escape and will heat the plastic. I also opted for fluorescent bulbs as they do not put out much heat. I thought the light that would be generated by flourescent bulbs would not be as appealing but it was actually much softer and nicer along with less heat. I hope this post helps others. We had many people interested in our home but we could not figure out the smell. Thanks, Kevin

This thread was a lifesaver for us too! We had the same symptoms, and after reading this, I determined it was the same thing -- the light fixture getting overheated, which produced a smell like a dead animal in our bathroom. For some reason we also thought this corresponded to rain outside, although I do not know how. Perhaps something to do with the humidity increases the smell factor? In our case we must have put in a 100w bulb a few months ago which is when the problem started, but it has been very intermittent.

It might be a good idea to take a Sharpie marker and write a note on the fixture (or inside so it's only seen when changing the bulb) to indicate the max. wattage of bulb to use. I'm surprised people don't burn down their houses putting overwattage bulbs in cheap plastic fixtures. And disappointed that these things can be manufactured and sold in the first place. Anyway, leave yourself a note, and the next owner too.

A Sharpie is handy around the house - write the filter size on the outside of the furnace, the date you last drained the water heater, etc.

Thankyou for this thread! We have just had a week of rain and high humidity and the house absolutely stunk like a dead animal. I could not figure out why it was in a few different places, and up high, not down low. We have those recessed downlights, and I would never have thought of it until I read this discussion. Spot on! Thx!

Do you people actually believe the "foul" and "dead animal" smell is coming from your recessed lights? If this were actually the case, why would you smell it specifically when there is rainfall?

Because when it rains, your kids play more downstairs therefore the lights are on at that time? Jesus.

Since when does melting plastic smell like fish or a dead rodent?

I have the same exact problem in my stairwell, and there are NO RECESSED LIGHTS THERE.

Guarantee most of you in time will realize that replacing the stupid lights did not solve your problem.

Haha, you sound happy. I smelt the near the bulbs, spot on. Took the bulbs out. No smell. I'm no scientist, just tellin' it how it is. You, my dear, might have a dead rat.

Just be aware that it could be something toxic. Do you have a basement with sewer drain pipe? If yes it could be something like this: rain wets some sewer vents or water clogs them with mud leafs trash and smell from sewer escapes in your basement. Make sure you put a bucket of water in drain pipe every 9 days. One more thing light a match and heat the thing you suspect reeks, you will quickly know if it's that or not. (example bulb)

When i installed fluorescent tubes i used a balast. WHEN BALAST WAS NEW FOR 1 WEEK THE ROOM REEKED AS IF YOU BURNED ROTTED VEGETABLES AND EVER SINCE THEN WHEN I GOT A NEW BALAST, I TURN ON THE TUBE WITH IT OUTSIDE IN MY SHED FOR 1 WEEK. The balasts i used are manufactured in Germany and France. So it's quite possible your stench is from bulbs.

I bet those stinking stairs are next to a wall built out of hollow blocks and that hollowness is as big as the wall is tall. You GOTTA break that thing or at least use a drill and drill 1 /2 in hole on about 7 places (don't drill one block on 7 places, every hole must be on about 2,6 to 4 feet distance and some shoud be lower and higher) AND SEE IF THE STENCH IS STRONGER. Make sure you come back AND WRITE HERE WHAT IT WAS ONCE YOU SOLVE YOUR PROBLEM! That environment can't be healthy for you nor your family so DEAL WITH IT.

To drill concrete/masonry/blocks/stone use Vidia head drill bits just go to local hardware store and buy one. Cool it of in a can of ordinary water after every hole.

To drill wood you can use HSS OR HSSCO (high speed steel cobalt) cool them of in machine oil.

Dear sfcreature, do you smell a rat? ;) Take notice, Zeke is not being objective, constructive or concerned primarily with his smell. He is simply trying to engage in a destructive conversation. Maybe lacking attention. Not the healthiest thing to feed. :/

wollfcubs, i understand Zeke's frustration:he's got that stench near his stairwell too. I do not think it is right that we judge him, you never know who may turn out to be of biggest help.

Zeke, tell us your story in details: when did it begin to stink, what you suspect it is, steps you have taken to deal with it, steps you wanted to take but you didn't for any reason, if you called a builder and / or expert what do they suspect on, laboratory analysis... c'mon, join us, we're all trying to figure out what it is, not to make fun out of each other's agony.

xfcreature, don't hold your breathe as wolf stated that was a drive by. It was his first post and he won't be back.............

of course i won't hold my breath... ...if there's a possibility that my writing helps anyone, i shall write. I wish we knew what the source of that horrid stench is.

millworkman, what do you suspect on, got any ideas?

i feel that this discovering of the source is so sloppy.

He is a troll trying to incite people, lol.

I'm back and I'm not a troll. I'm just irritated because I have the same problem as some of you have. But instead of falling into some weird delusional state about recessed lighting, I'm looking for real answers.

I bought the house in 2007 and i noticed the smell, here we are in 2016 and the same smell is there, sometimes it disappears and sometimes it comes back with a vengeance.

For a while I thought it was a dead rodent (thats what it smells like), but after a few years that seemed very unlikely.

The smell is most pronounced when it is rainy. The wetter the day, the more it smells. It's just embarassing because we rent out our room downstairs to a woman, and i think it sucks that she has to smell it.

In addition to the dead animal smell, I sometimes smell...toilet. A strong smell of urine.

I was sure the smell was coming from UNDER the stairs, but when i went into the garage and cut out a piece of the wall, stuck my head in the hole along with a flashlight, there was no smell, and absolutely nothing under the stairs.

The smell seems to come from the wall that separates our house from the next door neighbor's house (i live in San Francisco, our houses are all squeezed together). I asked my neighbor if he ever smells anything, he said no. So I assume it isn't the wall that joins the two houses.

I've never had a professional come look at the house. I don't even know who to ask. I've had plumbers and contractractors in the house for various reasons, and when I mention it to them, they just kinda blow me off.

But, maybe I should change my light-switches??? I have plastic light switches near the stairs--maybe light is reflecting off planet venus, getting magnified through my window, melting the light switches? That must be it, case closed, thank god I have the soccer moms on Houzz to help me solve this mystery!

I have lived 23 years in a 2 story house in the suburbs on north side of Houston, Texas. The house was built in 1970. The foundation is a concrete slab on grade.

A "skunk like" smell started after rains about a year ago, 2015, in 1st floor master bedroom, at the right front SW corner of house. There is no plumbing near the north wall of the house. The street is South of home. Plumbing drainage exits the home to the rear and flows north to a public gravity sewer line behind the house. (No septic tank or sump pump.)

Having read all of this thread, I still need a plan. I was hoping someone would tell me something like "pour chlorine along the edge of the slab in the area of the smell, to kill the smelly old that is activated by the rain", but alas ... Help!

I have a sour milk smell at the base of the stairs. Last week it smelled more like trash. This is a condo, so I thought the smell was coming from my neighbors' trash, which I think is in their garage on the other side of the wall, but now it smells like it's actually in the carpeting. I don't drink milk and neither does my husband, and it's relatively new carpet. Anyway, it's gross, and I am hoping it's not something that involves ripping out the wall or something, because we just bought the place and the idea of cutting into walls makes me queasy.

Confidential to Zeke: I lived in SF for many years in a 1909 Victorian that had about 6 inches between it and the house next door. I had a stink in a room that was on that outside wall (coming out of the defunct gas fireplace) that I thought might be gas so I called PG & E. The guy used his little detector wand and found nothing, but he said the smell was sewer gas wafting up in that teeny space between the houses and somehow getting caught in the space for the old gas pipes for the fireplace. Don't know the age of your house, but old houses there have been through many incarnations. There may be a weird feature (fireplace, dumbwaiter, laundry chute) that's been walled off and causing the stink to enter the house. Also, much plumbing in SF, as you're undoubtedly aware, is ancient and not exactly on stable ground so the obvious answer is plumbing. I've read that a toilet wax seal can be cracked and lead to a pee smell, and the other smell is possibly a vent (sewer gas vent) or a bad sewer pipe. Preferably the municipal one...

Check your electrical outlets and switches for heat. Just put your hand flat on the plate. Also sniff around any light fixtures in the area. Sometimes overheating plastic can give off odd odors. If you find a hot outlet, shut off the power and have it replaced immediately. They should not even be warm. If it's coming from a fixture, make sure the bulb is not overrated for the fixture and thus overheating it. Sometimes even the rated wattage of bulb can make a modern plastic fixture smell, so if it's that, switch to a low heat CFL or LED bulb or replace the fixture.

damn zeke you're a jerk

I know this is an older thread, but we have this exact same situation, only it is outside of our house. We moved in to the house in August 2022 and got our first rain in October. It has2 1/2 months and the smell has not fully gone away, and gets worse after every rain. No electrical out there, and the smell relatively comes from the same spot, but I can not pin point it. It is near PG&E and water department access boxes, but other than that, I don’t even know where to go from here… anyone?